Blasting cap



R. W CAIRNS Aug. s, 195o.

LAsTINc. CAP

' Filed April 10, 1946 ROBERTAWzAIRNS INVENTOR.

FIG. 4

AGENT Patented Aug. 8, 1950 BLASTING CAP Robert W. Cairns, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application April 10, 1946, Serial No. 660,921

(Cl. B-28) 10 Claims.

This invention relates to an improved iiring device and more particularly to blasting caps which have an increasedfactor of safety in regard to the positiveness of detonation. u l

The ring devices which are used in the art, such as blasting caps, either of the fuse or electric type, contain an explosive charge which may be pressed into the cap. In the fuse type it must be pressed in such a manner that there is no danger of it becoming loose or falling out. Blasting caps have been made in which the explosive, such as mercury fulminate, diazodinitrophenol, or the like, either alone or in admixture with an oxidizing agent. such as potassium chlorate, barium nitrate, lead dioxide and the like are used. These explosive charges are pressed within the shell and may, if desired, be enclosed by means of a copper capsule inserted into the shell. Normally, whenever a capsule is used. there is a small perforation in the top of the capsule to allow ignition of the explosive charge, and in most cases in order to insure ignition, a very thin wafer charge of an ignition compound is positioned and pressed into place on top of the capsuie.

In addition to the above, there are blasting caps on the market in which there is positioned in the bottom of the cap by a pressing operation a secondary explosive or base charge, such as, for example, tetryl (trinitrophenyl methyl nitramine), trinitrotoluene, nitrostarch, pentaerythritol tetranitrate, nitromannite, or picric-acid. superimposed upon the base charge is a priming charge, likewise pressed into position. The priming charge, readily ignitable by various ignition means, insures proper ignition of the base charge.

In the above type caps, the copper shell may be slightly varied in length and diameter but usually an inside diameter of about 0.21 inch to about 0.24 inch and a length of about 11/2 to about 1% inches are used for a No. 6 while the No. 8 caps may be of the same diameter but from 1A, to 3A inch longer. However, due to the small volume within the caps, it may be found difficult to include therein sufficient explosives to obtain the desired amount of detonating ability. In order to overcome this difficulty, the introduction of capsules to enclose the priming charge has been found to increase its efficiency. To further increase emciency of the priming charge, high pressures have been resorted to in pressing operations but pressures are limited due to the phenomenon known as dead pressing. Dead pressingl is well known in the explosive industry 56 and practically any of the explosives, while increasing in strength when subjected to pressure, reach a point where sensitivity to detonation by the application of a small amount of heat, such as that from a fuse, drops oif entirely. Thus mercury fulminate, a very sensitive material, can be pressed to a point where it will fail to detonate from the heat produced by the ignition means.

' This limitation to the pressure applied is a controlling factor in producing strong blasting caps.

It is the object of this invention to produce an improved iiring device.

It is a further object of this invention to provide an improved blasting cap in which dead pressing is easily avoided.

It is a further object of this invention to provide a blasting cap in which the use of a capsule is unnecessary.

It is a further object of this invention to provide a blasting cap which is easily and economically manufactured.

Other objects of the invention will appear hereinafter the novel features and combinations being set forth in the appended claims.

Generally described, the present invention comprises a blasting cap containing a pressed priming charge, the shell of the blasting 'cap having an indentation extending into'the priming charge at a position below the top of the charge. The indentation is placed in the shell before the priming charge is pressed.

The nature and purpose of this invention having been described in a general way, there follows a more detailed description of preferred embodiments thereof with reference to the accompanying drawings in which:

Fig. 1 is a longitudinal section of a fuse-type blasting cap having a circumferential indentation.

Fig. 2 is a cross-sectional view of a blasting cap having an intermittent circumferential indentation.

Fig. 3 is a longitudinal section of another-form of a fuse-type blasting cap having a circumferential indentation.

Fig. 4 is a longitudinal section of an electric blasting cap having a circumferential indentation.

In Fig. 1, a shell or casing I I of copper, bronze or other suitable material, contains an explosive charge I2 made up of a pressed base charge I3, such as pentaerythritol tetranitrate, tetryl, trinitrotoluene, nitrostarch, and similar explosives, and a pressed priming charge I 4, such as diazodinitrophenol. mercury fulminate, or Vthe like,

either alone or in admixture with an oxidizing agent, such as potassium chlorate, barium nitrate, lead dioxide. and the like. The shell Il has an open end adapted to receive a safety fuse I5. The shell wall has an indentation I6 positioned in the upperhalf of the priming charge, that is, between a point slightly below the top and above the mid-point of `the pressed priming charge I6. The indentation I6 may be a corrugation in and completely around the wall of the blasting cap or it may be a corrugation intermittently around the wail as shown in Fig. 2.

In Fig. 3, the shell or casing I I contains an explosive charge I2 which is made up of a pressed base charge I3 and a pressed priming charge I4 such as set forth for Fig. l. The shell II has an open end adapted to receive a safety fuse I5. The shell wall has an indentation I 6 which is positioned between a point below the top of the priming chargevand above the mid-point oi the pressed priming charge. The indentation i6 is a corrugation in and completely around the wall of the blasting cap. The inside diameter of the tip I1 of the shell ii which contains the base charge I3 is not more than the inside diameter charge I2 made up of a pressed base charge I3,

and a pressed priming charge I4 such as set forth for Fig. l. An ignition assembly comprising a plug I3 with leg wires I9 and a bridge Wire 20, is inserted into the shell II. The bridge wire 20 and terminal ends of leg wires I9 are embedded in a charge of ignition explosive 2|, such as an admixture of diazodinitrophenol and potassium' chlorate or other suitable ignition explosive. The indentation I6 is positioned similar to that describedin connection with Fig. l.

'I'he blasting caps of this Vinvention may be made by several methods. The base charge may be pressed in the shell either before or after the shell is indented. However, it is essential that the priming charge be pressed in the shell after before the base charge is added and the base charge is pressed with an undersized pin which will pass the corrugation. When this method is used, it is preferably to construct the shell as shown in Fig. 3 with the portion of the shell which contains the base charge having an inside diameter not greater than the inside diameter at the indentation.

The indentation may be discontinuous as shown in Flg.2 to provide a symmetrical arrangement around the shell. A pressing pin. preferably used in the loading of shells of this construction, has a narrow stem and a short cylindrical end portion of the diameter which is normally used with an undented shell. The end portion of the pin is provided with grooves compatible with the symmetrical indentation to permit passage into the shell. Accordingly, the base charge may be pressed a second time after giving the pin or the shell a partial turn about its axis after the grooves in the pin have cleared the symmetrical indentation. This procedure eliminates the small underpressed areas remaining after the initial pressing. said underpressed areas being caused by the aforementioned grooves in the pressing pin.

This invention is applicable to any blasting cap in which the priming charge isy pressed. Thus, in addition to the fuse-type caps and the electric blasting cap illustrated in the drawings, a matchhead or delay-type electric blasting cap may be greatly improved by use of this invention.

As a specific example of a fuse-type cap incorporating this invention, there were produced shells of 0.22 caliber having an indentation completely around the shell at a height of I5/n4 inch from the base of the shell. The inside diameter at the indentation was 0.208 inch. 'An undersized pressing pin was used to press a base charge of 0.22 gram of pentaerythritol tetranitrate to a height of m/fsi inch. A priming charge oi 0.40 gram of a 75 to 25 mixture of diazodinitrophenol and potassium chlorate was placed in the shell and pressed with a normal size pressing pin at the pressures given in the following table. Similar caps were pressed which had no indentation. The results of the plate tests are given 'in the following table.

In conducting the plate tests a blasting cap was placed upright upon and in themid'dle of an aluminum plate l inch square and 1A; inch thick. The plate was horizontally held in space by supports placed under the edges of the plate only. 'I'he performance of the blasting cap is indicated by the condition of the plate after firing. A cap making a hole in the plate is given an A" classiiication and a subnumeral as A5, As. etc., to indicate the diameter of the hole in millimeters. A D" classiiication indicates dead failure, as the cap is not destroyed and the plate is left unscarred.

With reference to the table, the numerals immediately preceding the classification letter indicate the number of caps tested and receiving the classification letter.

TABLE dented and with. regular shells Plate Test Pressure Regular Ind ted ell sneu sneu 3,000 5A; 4A lAl amo 4A.,1D 2.1i., ai. 4,000 BAA 4,500 4A.. 1A. 5,000 3A.

The results indicate that the indentations make it possible4 to apply a pressure in the order of 5000 lb./sq. in. or more to the priming charge before it is "dead pressed." whereas without the indentation the priming charge is "dead pressed" at 3500 lb./sq. in.

In drop out tests conducted to further determine the merits of the invention, open end caps were dropped 5 times each in an inverted position from a height of 28.5 inches upon a steel anvil. The weight of the guide in which the caps were dropped was 5.8 pounds and the caps were considered to have failed if any part oi' the charge was dislodged during the test. The drop out tests indicated a denite superiority of the caps with indentations in accordance with this invention as compared to similar caps without indentations.

The distance of the indentation from the bottom of the shell will depend upon the nature and quantity of the base charge, the nature and@ quantity of the intermediate charge or charges,

" ing pin and the amount of Vexplosive used vary with the type of explosive. size of the shell, and depth of the indentation.

The use of a shell with an indentation below the top of the priming charge and above the midpoint of the priming charge permits the use of a ,suflciently great force on the pressing pin used to press the priming charge to secure adequate strength and resistance to tapping-out without the danger of dead pressing. A much wider range of force on the pressing pin is operable with a shell having an indentation than with an ordinary shell with no indentation. Also a much wider range in the amount of priming charge may be used with blasting caps made in accordance with this invention than with blasting caps having no indentation.

The reasons for the improvements resulting from this invention are not perfectly understood. Howev'er, it is believed that when the pin is pressed down with a given force into the shell, the priming charge as a whole is compressed until the layer next to the wall and above the indentation oiers sufficient resistance to take substantially all the load. In this way, all of the material below the indentation and the part of the material in the central part of the cap above the indentation is less highly pressed than it otherwise would be. At the same time, the uppermost part of the charge near the shell wall is sufliciently well pressed against the wall to effectively resist tapping-out. and tapping-out is also resisted by the pressed, than caps having no indentation.

By the use of this invention, the necessity and desirability of the capsule within the cap shell is, eliminated. From a manufacturing standpoint, the caps without a capsule are much easier and safer to make and several loading and pressing operations are eliminated. Moreover, caps made in accordance with this invention will withstand a much greater pressure applied to the priming charge, without becoming dead pressed, than caps having no indentation.

What I claim and desire to protect by Letters Patent is:

1. A blasting cap having in combination va pressed explosive charge and a shell having an indentation extending into the upper half of the pressed explosive charge; the density of the central portion of the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition assembly while the density of the portion thereof above the indentation and adjacent the shell Wall is substantially higher than the density of the said other portions.

2. A blasting cap having in combination a pressed priming charge and a shell having a circumferential indentation extending into the -upper half of the priming charge; the density of the central portion of the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition assembly While the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

3. A blasting cap having in combination a pressed priming charge and a shell having an intermittent, circumferential indentation extending into the upper half of the priming charge; the density of the central portion of the pressed charge and the portion thereof below the indentation adjacent the shell wall being .below the point of' dead pressing forV the particular ignition assembly while the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

4; A blasting cap having in combination a pressed priming charge and a shell having an intermittent, symmetrical, circumferential indentation extending into the upper half of the priming charge; the density of the central portion of the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition assembly while the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

5. A blasting cap having in combination a pressed base charge, a pressed priming charge superimposed on the base charge,` and a shell having a bottom portion of reduced diameter surrounding the base charge and having a circumferential indentation extending into the upper half of the priming charge; said diameter being not more than the inside diameter of the shell at the indentation; and the density of the central portion of 'the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition assembly while the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

6. A blasting cap having in combination a pressed priming charge and a shell having an indentation of between about 0.003 inch and about 0.020 inch deep extending into the upper half of the priming charge; the density of the central portion of the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition assembly while the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

7. A blasting cap having in combination a pressed priming charge and a shell having an indentation of between about 0.003 inch and about 0.020 inch deep extending into the upper half of the priming charge at a point between 0.015 inch and 0.15 inch below the top of the priming charge; the density of the central portion of the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition aembly while the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

8. A blasting cap having in combination a tion and adjacent the shell wall is substantiallyhigher than the density of the said other portions.

9. A blasting cap having in combination a pressed priming charge comprising a mixture of diazodinitrophenol and potassium chlorate superimposed on a pressed base charge comprising pentaerythritol tetranitrate and a shell having an indentation of between about 0.003 inch and about 0.020 inchldeep extending into the upper half of the priming charge at a point between 0.015 inch and 0.15 inch below lthe topv of the priming charge; the density of the central portion of the pressed charge and the portion thereof below the indentationA adjacent the shell wall being below the point of dead pressing for the particular ignition assembly while the density o1' the portion thereof above the indentation and adjacent the shell Wall is substantially higher than the density of the said otherportions.

10. A blasting cap having in combination a. pressed priming charge comprising a mixture of diazodinitrophenol and potassium ohlorate superimposed on a pressed base charge compris- @eriicate of Patent No. 2,517,763

8 ing pentaerythritol tetranitrate and a shell having a bottom portion of reduced diameter surrounding said base'charge and having a circum- Ierential indentation of between about 0.003 inch and about 0.020 inch deep extending into the upper half of the priming charge at a point between 0.015 inch and 0.15 inch below the top of the priming charge; said reduced diameter being not more than the inside diameter of the shell at the indentation; and the density of the central portion ot the pressed charge and the portion thereof below the indentation adjacent the shell wall being below the point of dead pressing for the particular ignition assembly while the density of the portion thereof above the indentation and adjacent the shell wall is substantially higher than the density of the said other portions.

v ROBERT W. CAIRNS.

REFERENCES CITED The following references are of record in the iile of this patent:

'UNITED STATES PATENTS Number Name Date 1,928,204 Large Sept. 26, 1933 1,950,019 Biazzi Mar. 6, 1934 2,178,723 Forsyth Nov. 7, 1939 2,186,426 Nash Jan. 9, 1940 2,363,863 Hanley Nov. 28, 1944 2,424,374 Taylor et al. July 22, 1947 FOREIGN PATENTS Number Country Date 406 Great Britain Jan:v 31, 1878 579,281 Great Britain July 30, 1946 Correction August s, o

ROBERT .W. CAIRNS It is hereby certified that error appears in the printed specication of the above numbered patent requiring correction as follows:

Column 5, line 48, strike out presser-i, than caps having no and insert instead anchoring reject of the and that the said Letters Patent should beread as'corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of November, A. D. 1950.

[mtl

vTHOMAS F. MURPHY,

Assistant Commissioner of Patents. 

